BMI accounts for height and weight to give an indicator of potential weight-related health issues.

Researchers from the University of North Carolina (UNC) studied charts from 245 food allergic kids who visited UNC clinics between 2007 and 2011. Taking age into account, researchers then compared the height, weight and BMI of the food allergic kids to more than 4,500 kids without food allergies and about 200 kids with growth-impairing diseases such as cystic fibrosis.

The results were clear – after kids hit two years old, those with food allergies tended to have lower weights and BMIs than kids without allergies. Kids with multiple food allergies fared worse – those with three or more allergies had lower weights and BMIs than kids with only one or two food allergies, according to AAAAI.

The type of food allergy also matters – kids with milk allergies tended to present with the lowest weights and BMIs.

So what does all of this mean? Kids with food allergies have to endure more dietary rules than kids without allergies. Likewise, the more food allergies a child has, the more restrictions, researchers note.

Although the number of people who have food allergies is going up, the majority of all food allergic reactions – 90 percent – still are caused by just eight foods: peanuts, milk, eggs, soy, wheat, crustaceans, fish and tree nuts, such as hazelnuts and walnuts. Of these, peanuts are the leading cause of severe allergic reactions caused by food.

If a person with food allergies eats an allergenic food or food containing even tiny amounts of allergenic protein, it may trigger an immune response. These allergic reactions can range from mild symptoms, such as hives, to severe gastrointestinal and respiratory distress, including throat swelling and difficulty breathing.

The most severe reaction is anaphylactic shock, which can carry the symptoms of an allergic reaction, but is coupled with a dangerous drop in blood pressure. Anaphylactic shock can be fatal.